Ferroaxial Transitions in Glaserite-type Compounds: Database Screening, Phonon Calculations, and Experimental Verification

The so-called ferroaxial transition characterized by
a rotational
structural distortion that breaks a mirror symmetry has gained growing
interest in terms of a new class of ferroic state in crystalline materials.
RbFe(MoO4)2, which belongs to glaserite-type
compounds, X(□;1)Y(□;2)[M(TO4)2], is one of the most representative materials
showing a ferroaxial transition, i.e., ferroaxial materials. Considering
a variety of glaserite-type compounds, we expect that they provide
a good arena for ferroaxial materials. In this work, we explored new
ferroaxial materials by formula-based screening using a regular expression
search and the symmetry detection algorithm. As a result, we found
that a glaserite-type compound, K2Zr(PO4)2, is one of the promising candidates for ferroaxial materials.
Experimentally, we demonstrate that K2Zr(PO4)2 shows a ferroaxial transition at about 700 K, which
is well explained by ab initio phonon calculations.
The ferroaxial nature of K2Zr(PO4)2 is further confirmed by the observation of its domain structures
using a linear electrogyration effect, i.e., optical rotation in proportion
to an applied electric field. Our work provides an effective approach
to exploring ferroaxial materials.